The present invention is directed to a device for monitoring fluid flow in a conduit and, more particularly, to a device operable to detect inhomogeneities, such as gas bubbles, in liquid-filled pipes, to verify and record events of inhomogeneity and to activate an alarm and/or alarms under certain conditions and/or numbers of events of inhomogeneity.
In many industrial processes involving liquid flow, it is often highly important that the fluid flow be maintained at a certain predetermined homogeneous flow rate. For example, in refrigeration systems or other fluid heat transfer processes, gas bubbles in the fluid input line may result in an insufficient amount of refrigerant causing a less than adequate heat transfer or inefficiency in the operation of the system. A heat transfer deterioration is highly undesirable in that the system may ultimately be unable to maintain the storage temperature required for the products stored in the refrigeration system. Thus, it is an advantage to provide a means in the system whereby an operator may determine that the flow input is homogeneous and completely fills the volume of the input line.
Within the closed system of a refrigeration system, the thermodynamic equilibrium of the fluorocarbon coolant is constantly changing between the liquid and gaseous phase as the result of the variations in temperature and pressure that occur as the coolant circulates between the compressor and the evaporator. ##STR1## The coolant is usually in the liquid state under high pressure at the inlet conduit as it leaves the condenser and in the gaseous state under low pressure as it leaves the evaporator. However, under normal operation frequent frothing and surging does occur due to the rapid passage of gas bubbles. The presence of this frothing (Flash Gas) at the inlet conduit is caused by the pressure changes downstream during the defrost cycle and as one or more evaporators cycle on and off.
An advantage of the device to be described is that it will detect such thermodynamic changes, analyze the data and alert the operator within about 30 minutes if there is a leak or other malfunction that will ultimately result in an unsatisfactory storage temperature.
An important advantage of the present invention is that it can be used to monitor the flow and thermodynamic state of all known commercial refrigerants although the physical properties of such refrigerants vary widely.
Another advantage of the present invention in monitoring refrigeration systems or other fluid transfer processes is the early detection of leaks in the system or other abnormalities such as malfunctioning of the compressor or valves which malfunction would cause a change in the thermodynamic state of the coolant as it flows through the system. An obstruction in the drier filter would also be detected by the monitor of the present invention at an early stage.
The monitor to be described has particular application to large multiple (parallel) refrigeration units of up to 240 horse power that are found in large supermarkets. A small leak, if not detected early, can result in the release of large amounts (hundreds of pounds) of chlorofluorocarbons into the atmosphere.
The present invention will also have a favorable environmental impact. In 1974, Sherwood Rowland and Mario Molina of the Irving Campus of the University of California, first warned that chloroflorocarbons might seriously damage the ozone layer in the stratosphere. In 1985 a team of British scientists announced the disconcerting news that the springtime ozone had diminished to nearly half of what they had measured a few years before. Two-thirds of the springtime ozone over Antarctica is now missing. There is a hole in the Antarctic ozone layer. It has shown up every spring since the late 1970's. While it heals itself in winter, the hole seems to last longer each spring.
Concern that a depletion of the ozone layer will increase the incidence of skin cancer and eye cataracts among the world population is such that the United States along with Canada and Scandanavian countries voluntarily ended the use of chlorofluorocarbons in aerosol sprays during the 1970's. In September of 1987, many of the nations that use and produce chloroflorocarbons met in Montreal to consider the possibility of an agreement to limit chlorofluorocarbon use. Now 37 nations including the USSR have agreed to a schedule of cutbacks in chlorofluorocarbon production, so that by 1989 production reverts to 1986 levels, and by 1999 to about 50 percent of that.
An early prior art proposal for the detection of gas bubbles in a refrigeration system inlet line comprises a sight glass to enable visual observation of the fluid flow. This approach has significant drawbacks in that it requires constant observation by an operator. Indeed, comprehensive monitoring of the system through the use of a sight glass is impractical since it is not economically feasible to maintain constant, round-the-clock surveillance by a human operator. The sight glass, at most, enables a spot check on the system to perhaps verify other indications of refrigerant insufficiency. Moreover, the use of a sight glass may not be feasible in certain applications such as refrigeration systems mounted on motor vehicles and in home air conditioners.
A second, more sophisticated proposal, utilizes wave energy transmissions such as ultrasonic sound waves which are transmitted through the fluid flow as a means to detect impurities, e.g., gas bubbles in a liquid refrigerant. An example of a device based upon the wave energy transmission approach is disclosed in U.S. Pat. Nos. 4,235,095 and 4,138,879. The prior device includes a pair of electromechanical transducers which are mounted upon the refrigerant inlet line in an acoustically coupled relationship. One of the transducers is operated to transmit ultrasonic sound waves through the inlet line. The other transducer is utilized to receive the transmitted ultrasonic sound waves and to convert the received waves into a electrical signal.
In accordance with the theory of operation of the disclosed device, the sound conductivity of the fluid flow within the input line will be a function of the material content of the line. Under normal operating conditions, the fluid line will contain only the refrigerant and transmit the sound waves according to the refrigerants's inherent sound conductivity properties. When impurities such as gas bubbles flow through the line, the conductivity of the fluid flow will be altered by the presence of gas pockets within the inlet line thereby varying the intensity of the ultrasonic sound waves received by the receiving transducer. This, in turn, will vary the electrical signal produced by the receiving transducer to indicate impurities in the inlet line.
Thus, the prior art proposal does provide a device for the detection of gas bubbles in a refrigerant but operates in a different manner (the driving signal to the transmitting transducer is increased as gas bubbles pass this transducer. Moreover, the apparatus described in U.S. Pat. Nos. 4,235,095 and 4,138,897 require temperature sensors at the input and output of the evaporator and a differential temperature indicating circuit to interpret the output of the device described and claimed.
Another shortcoming of the heretofore known wave transmission devices is that the impurity detection merely indicates the presence of impurities, such as gas bubbles, at the instances of occurrence and does not provide information critical to the comprehensive monitoring of the refrigeration system over time. The operation of devices known prior to our invention might notify an operator of the flow of gas bubbles through the inlet line but does not give any indication as to whether the gas flow is a momentary and not untypical abberation in refrigerant flow or a significant event of refrigerant insufficiency adversely effecting efficient operation of the system.
It is a primary objective of the invention to provide a wave transmission type impurity indicator which not only detects and indicates the presence of impurities in the fluid flow, but also verifies the occurrence of significant events of inhomogeneity in fluid flow, records the number of significant events within a predetermined period of operation of the system and compares the number of recorded events to a predetermined acceptable maximum number of events.
Another object of this invention is to notify the operator of a single significant event, the duration of which exceeds 30 minutes.